For example, in a wire harness for a vehicle such as an automobile, etc., an operation for joining conductors of a plurality of insulated wires together has been carried out.
As a technique for joining the conductors of the plurality of wires, there is known a technique of increasing peel strength at a joining region in such a way that conductors exposed from insulated wires are bundled by a metallic foil and then joined by an ultrasonic joining (see PTL 1, for example).